Cimetidine decreases theophylline elimination II

ABSTRACT

This study examines the effect of intravenous cimetidine administration on aminophylline elimination. Aminophylline [4.3 mg/kg] was administered by short intravenous infusion both before and after cimetidine administration. Cimetidine was administered by exponential infusion system to achieve and maintain a concentration of 4.0 micro g/mI in the plasma. Plasma samples were collected before and at various hours for 12 hours after each aminophylline administration, and theophylline concentrations were measured by an HPLC system. Cimetidine significantly decreased theophylline clearance p < 0.03, and increased theophylline elimination half life p < 0.05. The apparent volume of distribution was not altered by cimetidine administration. Cimetidine may slow theophylline elimination by inhibition of the hepatic microsomal monoxygenase system, which could be clinically significant and cause serious side effects. The effect of cimetidine on metabolic pathways of theophylline is the objective of future study